PURPOSE: To reduce the power consumption at low speed operation by adopting the constitution that no current flows to an inverting amplifier for high speed oscillation at the low speed oscillation.

CONSTITUTION: An N-channel MOS transistor (TR) (12c) and a P-channel MOS TR (12d) turned off at the low speed oscillation, the inverting amplifier for the high speed oscillation does not give any effect on the circuit operation and no power is consumed. An input voltage to a inverting amplifier for the low speed oscillation consisting of an N-channel MOS TR (11a) and a P-channel MOS TR (11b) descends or rises gradually by a time constant comprising a feedback static capacitor 3 and a feedback resistor 4 from a power voltage or a common potential as shown in figure (a), and the moment the voltage reaches a threshold value of the inverting amplifier for the low speed oscillation, the output of the feedback inverting amplifier comprising an N-channel MOS TR (2a) and a P-channel MOS TR (2b) is inverted, a positive feedback is given through the feedback static capacitor 3 thereby causing the output to be descended or boosted momentarily to the common potential or the power voltage. The operation above is repeated to cause the oscillation.